On Mon, 22 Aug 2016, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> On Mon, Aug 22, 2016 at 03:09:48PM +0300, Jani Nikula wrote:
>>
>> On Mon, 22 Aug 2016, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
>> > [ 284.922349] ======================================================
>> > [ 284.922355] [ INFO: possible circular locking dependency detected ]
>> > [ 284.922361] 4.8.0-rc2+ #430 Tainted: G W
>> > [ 284.922366] -------------------------------------------------------
>> > [ 284.922371] cat/1197 is trying to acquire lock:
>> > [ 284.922376] (&dev->filelist_mutex){+.+...}, at: [<ffffffffa0055ba2>] i915_ppgtt_info+0x82/0x390 [i915]
>> > [ 284.922423]
>> > [ 284.922423] but task is already holding lock:
>> > [ 284.922429] (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0055b55>] i915_ppgtt_info+0x35/0x390 [i915]
>> > [ 284.922465]
>> > [ 284.922465] which lock already depends on the new lock.
>> > [ 284.922465]
>> > [ 284.922471]
>> > [ 284.922471] the existing dependency chain (in reverse order) is:
>> > [ 284.922477]
>> > -> #1 (&dev->struct_mutex){+.+.+.}:
>> > [ 284.922493] [<ffffffff81087710>] lock_acquire+0x60/0x80
>> > [ 284.922505] [<ffffffff8143e96f>] mutex_lock_nested+0x5f/0x360
>> > [ 284.922520] [<ffffffffa004f877>] print_context_stats+0x37/0xf0 [i915]
>> > [ 284.922549] [<ffffffffa00535f5>] i915_gem_object_info+0x265/0x490 [i915]
>> > [ 284.922581] [<ffffffff81144491>] seq_read+0xe1/0x3b0
>> > [ 284.922592] [<ffffffff811f77b3>] full_proxy_read+0x83/0xb0
>> > [ 284.922604] [<ffffffff8111ba03>] __vfs_read+0x23/0x110
>> > [ 284.922616] [<ffffffff8111c9b9>] vfs_read+0x89/0x110
>> > [ 284.922626] [<ffffffff8111dbf4>] SyS_read+0x44/0xa0
>> > [ 284.922636] [<ffffffff81442be9>] entry_SYSCALL_64_fastpath+0x1c/0xac
>> > [ 284.922648]
>> > -> #0 (&dev->filelist_mutex){+.+...}:
>> > [ 284.922667] [<ffffffff810871fc>] __lock_acquire+0x10fc/0x1270
>> > [ 284.922678] [<ffffffff81087710>] lock_acquire+0x60/0x80
>> > [ 284.922689] [<ffffffff8143e96f>] mutex_lock_nested+0x5f/0x360
>> > [ 284.922701] [<ffffffffa0055ba2>] i915_ppgtt_info+0x82/0x390 [i915]
>> > [ 284.922729] [<ffffffff81144491>] seq_read+0xe1/0x3b0
>> > [ 284.922739] [<ffffffff811f77b3>] full_proxy_read+0x83/0xb0
>> > [ 284.922750] [<ffffffff8111ba03>] __vfs_read+0x23/0x110
>> > [ 284.922761] [<ffffffff8111c9b9>] vfs_read+0x89/0x110
>> > [ 284.922771] [<ffffffff8111dbf4>] SyS_read+0x44/0xa0
>> > [ 284.922781] [<ffffffff81442be9>] entry_SYSCALL_64_fastpath+0x1c/0xac
>> > [ 284.922793]
>> > [ 284.922793] other info that might help us debug this:
>> > [ 284.922793]
>> > [ 284.922809] Possible unsafe locking scenario:
>> > [ 284.922809]
>> > [ 284.922818] CPU0 CPU1
>> > [ 284.922825] ---- ----
>> > [ 284.922831] lock(&dev->struct_mutex);
>> > [ 284.922842] lock(&dev->filelist_mutex);
>> > [ 284.922854] lock(&dev->struct_mutex);
>> > [ 284.922865] lock(&dev->filelist_mutex);
>> > [ 284.922875]
>> > [ 284.922875] *** DEADLOCK ***
>> > [ 284.922875]
>> > [ 284.922888] 3 locks held by cat/1197:
>> > [ 284.922895] #0: (debugfs_srcu){......}, at: [<ffffffff811f7730>] full_proxy_read+0x0/0xb0
>> > [ 284.922919] #1: (&p->lock){+.+.+.}, at: [<ffffffff811443e8>] seq_read+0x38/0x3b0
>> > [ 284.922942] #2: (&dev->struct_mutex){+.+.+.}, at: [<ffffffffa0055b55>] i915_ppgtt_info+0x35/0x390 [i915]
>> > [ 284.922983]
>>
>> Do we have a regressing commit reference?
>
> For an unlikely ABBA debugfs deadlock that no one reported?
Of course, that one line in the commit message would have been
sufficient for me to not ask...
BR,
Jani.
>
> 1d2ac403ae3bfde7c50328ee0d39d3fb3d8d9823
> drm: Protect dev->filelist with its own mutex
>
> -Chris
--
Jani Nikula, Intel Open Source Technology Center
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